The invention relates to a method and a device for compensating for propagation delay differences between n serial data streams (n=2, 3, . . . ), which are each transmitted via parallel optical lines, with data which can be transmitted by means of the n serial data streams being in the form of m-bit-words (m=1, 2, . . . ).
Cables which have a number of optical lines can be used for optical transmission of information and data. The lines are in this case in the form of individual glass fibers. When data is transmitted in parallel form and optically via a number of glass fibers, which are combined to form a cable, the signals to be transmitted have different delays in the individual glass fibers. These delays are due to physical effects and relate, in particular, to propagation delay scatters owing to wavelength differences or manufacturing tolerances, which occur during the production of the glass fibers. This places a major restriction on the maximum length of the glass fibers that can be used for transmission. For example, the maximum length for transmission of data rates of 1.3 GBd is less than 100 m.
In order to avoid propagation delay differences resulting from manufacturing tolerances in the production of the glass fibers, the glass fibers that are produced are measured individually and are then selected such that only glass fibers with similar transmission characteristics are used together in one cable.
U.S. Pat. No. 5,426,644 (European patent 533 091) describes a method for parallel transmission of data, with a large number of 1 to P parallel data channels at the transmission end being in each case converted by means of a multiplexing apparatus as a serial data stream and then being transmitted to the receiver end, where the serial data is once again demultiplexed in an appropriate manner. This system has a propagation delay compensation apparatus, which synchronizes the serial data.
In the article xe2x80x9cLong Distance Parallel Data Link Using WDM Transmission with Bit-Skew Compensationxe2x80x9d, from the Journal of Lightwave Technology, Vol. 14, No. 5, May 1996, G. Jeong, et al. describe, as an alternative to pure serial data transmission systems for long distances ( greater than  greater than 10 km), a parallel WDM data transmission system with a propagation delay compensation apparatus. The disclosed methods for compensating for propagation delay between the parallel optical data channels have the disadvantage that it is necessary to measure the propagation delay differences between the various parallel transmission channels individually.
It is accordingly an object of the invention to provide a device and method for compensating for propagation delay, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which compensates for the described propagation delay scatters, which, in particular, does not require separate propagation delay characterization of the parallel transmission channels.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for compensating for propagation delay differences between n serial data streams transmitted via parallel optical lines, wherein the data transmitted via the n serial data streams are formed as m-bit words, the device comprising:
n regeneration apparatus each having an input connected to one of the parallel optical lines, a data output and a clock output, the input receiving a data stream from the respective optical line, each the regeneration apparatus being configured to regenerate data and a clock from the respective data stream;
propagation delay control apparatus each having a data input and a clock input respectively connected to the data output and the clock output of the regeneration apparatus, the data input receiving the regenerated data and the clock input receiving the regenerated clock; and
each of the propagation delay control apparatus having a demultiplexer for dividing the regenerated data and the regenerated clocks in a ratio 1:(xxc2x7m) and an alignment apparatus for distributing the divided, regenerated data between in each case xxc2x7m parallel data outputs of the propagation delay control apparatus, wherein a divided, regenerated clock that is synchronized to the divided, regenerated data is emitted at a clock output of a least one of the propagation delay control apparatus.
In other words, the objects of the invention are achieved:
in that data and a clock for the respective data stream are regenerated by means of the respective regeneration apparatus, with the data stream being transmitted via the parallel optical lines to the respective input;
in that one data output and one clock output of the regeneration apparatus are in each case connected to propagation delay control apparatus, so that the regenerated data and the regenerated clock are respectively passed to a data input and a clock input of the propagation delay control apparatus; and
in that the propagation delay control apparatus each have a demultiplexer for dividing the regenerated data and the regenerated clocks in the ratio 1:(xxc2x7m) (x=1, 2, . . . ) and an alignment apparatus for distributing the divided, regenerated data between in each case xxc2x7m parallel data outputs of the propagation delay control apparatus, wherein a divided, regenerated clock which is synchronized to the divided, regenerated data can be emitted at a clock output of a least one of the propagation delay control apparatus.
It is a primary advantage of the invention that it provides the capability to compensate for the propagation delay scatters which occur during transmission by means of parallel optical lines. In comparison to known transmission paths, this allows considerably longer transmission paths to be used. This opens up novel application options for the use of optical signals for information transmission.
A further advantage is that there is no need for measurement and selection of glass fibers which have been produced and are intended to be used together in one glass fiber, since any propagation delay differences that occur can be compensated for by means of the device according to the invention.
In accordance with an added feature of the invention, the n regeneration apparatus are a clock regeneration apparatus.
In accordance with an alternative feature of the invention, one of the n regeneration apparatus is a clock regeneration apparatus, and a number nxe2x88x921 of the regeneration apparatus are each formed as a phase regeneration apparatus, and the clock output of the clock regeneration apparatus is connected to a respective clock input of the nxe2x88x921 phase regeneration apparatus.
In accordance with another feature of the invention, the device further comprises:
n multiplexer apparatus for converting the divided, regenerated data to a respective serial, regenerated data stream, the n multiplexer apparatus having xxc2x7m parallel data inputs respectively connected to the xxc2x7m parallel data outputs of the propagation delay control apparatus; and
a synthesizer having an input connected to a respective clock input of the multiplexer apparatus and to the clock output of the at least one propagation delay control apparatus, and the synthesizer having an output connected to a respective further clock input of the multiplexer apparatus.
In accordance with an additional feature of the invention, at least one of the n multiplexer apparatus has a serial clock output for outputting a further serial clock signal matched to the serial regenerated data stream and delayed with respect to a serial clock signal generated by the synthesizer.
In accordance with a concomitant feature of the invention, decoder apparatus are provided. Each of the decoders is coupled between a respective propagation delay control apparatus and multiplexer apparatus.
That is, one expedient refinement of the invention provides that the n regeneration apparatus are each in the form of a clock regeneration apparatus, thus allowing separate clock regeneration for each of the parallel optical lines. One development of the invention provides that one of the n regeneration apparatus is in the form of a clock regeneration apparatus, and in that nxe2x88x921 regeneration apparatus are each in the form of phase regeneration apparatus, wherein the clock output of the clock regeneration apparatus is connected to a respective clock input of the nxe2x88x921 phase regeneration apparatus. This makes it possible to save nxe2x88x921 clock regenerators, since only one phase matching process takes place in the nxe2x88x921 phase regeneration apparatus, using the clock which is regenerated by means of the clock regeneration apparatus.
In a further development of the invention, n multiplexers for converting the divided, regenerated data to a respective serial, regenerated data stream are provided, as well as a synthesizer. The xxc2x7m parallel data outputs of the propagation delay control apparatus are respectively connected to xxc2x7m parallel data inputs of the n multiplexers, wherein the input of the synthesizer is connected to a respective clock input of the multiplexers and to the clock output of the at least one propagation delay control apparatus. One output of the synthesizer is connected to a respective clock input of the multiplexers. This makes it possible to convert the parallel data, whose propagation delay scatters have been compensated for, to a serial data stream for further processing.
It is expediently possible to provide for at least one of the n multiplexer apparatus to have a serial clock output, wherein a further serial clock signal can be emitted via the serial clock output, which further serial clock signal is matched to the serial regenerated data stream and is delayed with respect to a serial clock signal which can be produced by means of the synthesizer. This allows a serial clock signal to be provided, which can be used for further processing of the serial regenerated data stream.
In order to allow the data to be decoded, it is possible to provide for a decoder apparatus to in each case be coupled between the propagation delay control apparatus and the multiplexer apparatus.
With the above and other objects in view there is also provided, in accordance with the invention, a method of compensating for propagation delay differences, which comprises:
receiving data with n regeneration apparatus arriving in n serial data streams via respective parallel optical lines, wherein data transmitted via the n serial data streams are in the form of m-bit words;
regenerating the data and a clock for the data received in each of the respective n regeneration apparatus; transmitting the regenerated data and the regenerated clock to a respective propagation delay control apparatus;
dividing the regenerated data and the regenerated clock in a ratio 1:(xxc2x7m) with a respective demultiplexer; and
distributing the divided regenerated data between parallel data outputs of the respective propagation delay control apparatus.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device and method for compensating for propagation delay, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.